The present invention relates to a pointer illuminating structure in a measuring instrument.
Heretofore, a pointer illuminating structure has been demanded for improving the visuality of a measuring instrument when used during the night or for some reason concerned with design.
As conventional pointer illuminating structures, there are such devices as shown in FIGS. 1 to 3, of which FIGS. 1 and 3 are perspective views of different conventional pointer illuminating structures and FIG. 2 is a sectional view of the structure of FIG. 1 as mounted to a measuring instrument.
In FIG. 1, the numeral 6 denotes a pointer having a fore end portion 10 and a rear end portion 12, with a pointer cap 5 being fitted over an intermediate portion between the fore end portion 10 and the rear end portion 12 to cover that portion of the pointer 6. The numeral 7 denotes a pointer support shaft.
Operation of the conventional structure of FIG. 1 will now be described with reference to FIG. 2. The numeral 2 denotes a dial plate of measuring instrument (not shown). Light is radiated directly from a light source (not shown) to a photoconductive plate 4 which is attached to the back of the dial plate 2. The radiated light is incident upon the circumference of a central light receiving portion 7 which is opposed to the photoconductive plate 4, then this incident light is reflected as indicated with arrows in FIG. 2 by a conical reflective surface 34 formed in the central light receiving portion and reaches the fore and rear end portions 10 and 12 of the pointer 6 to illuminate those portions.
In the structure of FIG. 3, the pointer 6 has only the fore end portion 10, not having the rear end portion 12, but the operation is the same as above.
In those conventional devices having such constructions and functions, however, since the pointer cap 5 for the prevention of light leak is sure to be fitted over the pointer 6, the luminous portion of the pointer 6 is scissioned by the pointer cap 5, thus making it impossible to illuminate the entirety of the pointer 6. That is, the visuality in nighttime use is low, and also in point of design, there are restrictions.